1. Field of the Invention
This invention relates to a method of and an apparatus for controlling the shape of a rolled material on a multi-high rolling mill such as, for example, a 12-high or 20-high rolling mill in which automatic strip thickness control and automatic strip shape control are performed in the rolling of a strip.
2. Description of the Prior Art
In recent years, in the rolling of a strip of a copper alloy or the like, not only is automatic strip thickness control executed on a multi-high rolling mill in order to meet a requirement for accuracy in strip thickness, but also a high degree of accuracy is required for the shape of a strip and accordingly an automatic shape controlling method has been developed.
For example, in a rolling mill of the type wherein a strip thickness is controlled with a roll depressing position while a shape is controlled with a forcing amount of backup rolls or a shifting amount of taper rolls, strip shape control is conventionally executed such that a shape of a strip in a widthwise direction (elongation of a rolled material in the rolling direction) is approximated with a quadric expression in response to a signal from strip shape meters. Coefficients of individual terms of the quadric expression are divided into symmetrical components and asymmetrical components to fix a shape and strip shape controlling actuators are operated in accordance with such components (Japanese Patent Laid-Open No. 54-151066. Japanese Patent Laid-Open No. 55-19401. Japanese Patent Laid-Open No. 55-42144). It is also a common practice that a change in strip thickness caused by a change in operation amount of such strip shape controlling actuators is forecast and a roll depressing position is modified in accordance with a predetermined calculation expression to prevent a change in strip shape (Japanese Patent Laid-Open No. 60-3908. Japanese Patent Laid-Open No. 60-3909).
However, since work rolls in a multi-high rolling mill are small in diameter, a complicated composite elongation including edge wave, a center buckle and so forth often takes place in a shape of a strip. Accordingly, if fixation of a shape of a rolled material is performed and controlled on a multi-high rolling mill involving such an approximation with a quadric expression as described above, sufficiently good shape control cannot be attained.
On the other hand, when the strip shape controlling actuators are operated, even if a change in strip thickness is forecast to change the roll depressing position, a vicious cycle takes place wherein also the shape changes as the roll depressing position changes. Accordingly, there is another problem that control cannot be attained with a high degree of accuracy.
Further, when the condition of a shape is remarkably bad such as at an initial stage of rolling, the level of signals outputted from shape controlling devices to shape controlling actuators is so high that some of the actuators may not follow a target signal from a restriction arising from a response characteristic. As a result, there is a further problem that the improvement in shape is delayed.
Further, in case noise is involved in a strip shape from a shape detecting device at each point of time, it is also desired to eliminate a possible error in operation which may be caused by such noise.
Meanwhile, a multi-high rolling mill has been developed which includes, in order to control the shape of a rolled material in a widthwise direction finely and accurately, a crown controlling device which includes a mechanism wherein a plurality of axially divided backup rolls are supported by means of saddles such that the forcing amounts of the individual divided backup rolls can be adjusted individually by way of the saddles and which locally controls the forcing amounts of the individual backup rolls to control the crown shape of a rolled material, an inclined depression controlling device which includes depressing driving mechanisms on the driving side and the working side so that the gap between upper and lower work rolls may be relatively adjusted between the driving side and the working side, and a lateral controlling device wherein intermediate rolls having tapers at the opposite end portions thereof are provided for axial movement in order to change deflections at the opposite end portions of the work rolls and the axial (lateral) positions of the intermediate rolls are adjusted.
Each of the controlling devices listed above operates as a strip shape controlling device for controlling the strip shape of a rolled material, and the strip shape of a rolled material is controlled finely and accurately by adjusting an operation amount of a strip shape controlling actuator with each of the controlling devices, that is, by adjusting a forcing amount of each of the divided backup rollers, a relative gap between the upper and lower work rolls on the driving side and the working side, and the axial positions of the intermediate rolls.
However, in such a multi-high rolling mill, if an operation amount of a strip shape controlling actuator is adjusted with a shape controlling device in order to control the shape of a rolled material, not only the strip shape of the rolled material is changed, but also an influence of the same is had on the outgoing side strip thickness of the rolled material, which will result in variation of the strip thickness. Consequently, there is a problem that control with a high degree of accuracy cannot be attained.